This application relates to a separation nut for retaining a bolt or threaded element of structure in assembly with articles of structure which must be separated from other structure without generating a release shock force.
In the field of scientific exploration and experiment there is often a need to separate packages of instrumentation, stages of propulsion units, parts of structure or experiments that are located in remote or hostile environments. Systems to cause the separation often incorporate explosive charges which actually fracture bolt members or use explosive squibs to generate shock and propulsive gases which act to disassemble bolts or studs to which threaded elements are engaged by segmented internally threaded fasteners called segmented nuts.
Bunker U.S. Pat. No. 3,926,090 issued Dec. 16, 1975 is hereby incorporated in its entirety by reference for showing of segmented nuts in a separation nut. Of interest to this subject invention is an article produced by TiNi Alloy Company 1144 65th Street, Unit A, Oakland, Calif., which is called the Frangibolt. This separation device utilizes a frangible bolt in combination with a Shape Memory Alloy spacer (SMA). The SMA spacer is applied directly around the shank of a bolt to fracture the bolt shank through a weakening groove. Application of heat through a circumferential heater to the Shape Memory Alloy spacer increases the length of the spacer to overload the bolt and cause it to fracture along a plane defined by the grooved shank diameter. Fracture of the bolt material under high stresses produces a high shock load due to release of the high induced stress to fracture the bolt. Large shock loads are also produced when an explosive charge is placed within the diameter of a bolt to fracture along a similarly grooved shank. Multipart separation nuts which operate by explosive force can generate shock loads which can include the impact on the assembly housing the released segments, the shearing or other causes of failure of assembly components to release the segments, and the dissipation of the explosive energy due to initiation of a squib or other explosive chemical assembly.
Various schemes have been used for the reduction of release shock which include passive damping by use of cushions, active damping which uses deformable members, increased movement of parts to dissipate energy, and pressurized housings to counteract motion and force. None of the above approaches the problem of relieving the stored strain energy in the bolt or threaded element and the assembled structure over a controlled period of time, thereby reducing the shock load.